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In recent years, body scanner technologies based on millimeter-wave and terahertz technologies have been shown to improve security in areas sensitive to terrorist attacks by detecting hazardous objects hidden underneath the clothing of people. Inevitably, useful devices have to provide an adequate compromise between spatial resolution limited due to diffraction and penetration through clothing. Within this context, the spectral absorption of a wide range of fabric, interference caused by the texture, and the effect of moisture within the fabric have to be considered. We have studied these effects by time-domain and Fourier transformation spectroscopy. The experimental findings are verified using a passive THz security camera operating in two frequency bands at 0.85 and 0.35 THz. The latter band was proven to be of superior use for security checks as it provides useful results even in cases of wet clothes.

Extraordinary optical transmission and perfect absorption are two plasmonic-based optical phenomenona that are both accompanied by high local field enhancements that can be exploited for biological and chemical sensing. Here we merge both phenomenona in a slit array metamaterial perfect absorber consisting of a dielectric layer sandwiched between two metallic layers of which the upper layer is perforated with a periodic array of slits. Period and dimensions of the slits and thickness of the dielectric layer are tuned in a way that virtually all light of a certain wavelength incident on the surface passes through the slits and is subsequently absorbed. As a consequence, light–matter interaction is greatly enhanced in the slits. Thus, already small concentrations of analytes down to a monolayer attached to the sidewalls of the slits can be detected by refractive index sensing and identified by their spectral fingerprints with a standard mid-infrared lab spectrometer.

An optical metamaterial, operating in between the MID/IR and the visible domain, which uses the effect of extreme coupling between closely spaced nanostructured gold metal plates and a planar gold substrate was realized by means of electron beam lithography and lift-off technique. This regime is only accessible by using an ultrathin oxide layer between metal plates and substrate, where the oxide layerisrealized by atomic layer deposition here. The involved fabrication is discussed in detail. The metamaterial shows the predicted effect of perfect absorption with multiple resonances in the spectral range from 100 THz to 600 THz. The plasmonic based resonance frequencies are very sensitive to the plate size of the grating and the spacer thickness.

Thermopile detectors are particularly well suited for spectral imaging, space science applications, track recording, presence detection and applications with low energy consumption. The purpose of this work is the fabrication of a surface-micromachined 2-D high detectivity thermopile array using a highly effective BiSb/Sb thermocouple materials combination. The thermoelectric array is built on 8x8 pixels with an active area of [email protected] in square, which are wired directly. Thermopile structure and absorber area are manufactured upon a sacrificial layer based on polyimide, which is removed at the end of the manufacturing process. Thermoelectric layers as well as wiring layers has been patterned almost exclusively by lift-off technique in order to obtain very small structure dimension with high reliability as well as high integration level. The active area of detectors can be equipped with two absorber types for different application, a broadband colloidal silver black layer as well as a quarter wavelength arrangement for the MIR wavelength range from 8 to [email protected] The detectivity of so manufactured FPAs is about 1x10^9 Jones exceeding most of the state-of-the-art thermopile detectors.

We present the concept and experimental set-up of a passive submillimeter-wave stand-off imaging system for security applications. Our ambition is the design of an application-ready and user-friendly camera providing high sensitivity and high spatial resolution at video frame rates. As an intermediate step towards this goal, the current prototype already achieves a frame rate of 10 frames per second and a spatial resolution below 2 cm at 8 m distance. The camera is the result of a continuous development and a unique concept that yielded first high-resolution passive submillimeter-wave images provided by cryogenic sensors in May et al. (2007). It is based on an array of 20 superconducting transition-edge sensors operated at a temperature of 450 mK, a closed-cycle cooling system, a Cassegrain-type optics with a 50 cm main mirror, and an opto-mechanical scanner. Its outstanding features are the scanning solution allowing for high frame rates and the compact and integrated system design.

A unique system for geomagnetic archaeometry is presented. It uses extremely sensitive superconducting quantum interference devices (SQUIDs) as magnetic field sensors, laid out as intrinsic gradiometers. These sensors are mounted on a non-metallic cart, which guarantees smooth movement even at high speeds. Using a differential global positioning system (GPS) together with an inertial system the measured magnetic field gradient data are located on the mapped area with centimetre resolution and the height profile is also provided using the GPS. All data are stored in a data logger and partially online displayed on a laptop computer. At the time of this report, the system is pushed manually and has been tested on a Neolithic double ring ditch near Weimar, Germany. In a gateway through the rings, remains of palisades and buildings have been well resolved, confirming the high sensitivity of the SQUID-based system. An excavation at the ring ditch showed that material with enhanced susceptibility was the origin of the magnetic field gradient signals. Copyright © 2007 John Wiley & Sons, Ltd.

An integrated gradiometer system is presented, consisting of a single-layer high-temperature superconductor dc superconducting quantum interference device (SQUID) and two coils, realized on printed circuit boards. The coils compensate the homogeneous background field, thus allowing the gradiometer to be freely moved in the Earth's magnetic field. The gradiometer signal is not harmed by any additional noise introduced by the homogeneous field compensation. Therefore, a noise-limited magnetic field gradient resolution of 15 pT m−1 Hz−1/2 with a 1/f corner frequency of 2 Hz was achieved. This is preserved even after motion in the Earth's magnetic field. Because of the small dimensions of the compensation coils, the gradiometer system can also be used for non-destructive evaluation. Preliminary measurements were performed by moving the SQUID across a workpiece, without any shielding.

We developed a gradiometer system based on a single-layer high-temperature superconductor dc superconducting quantum interference device (SQUID), which can be freely moved within the Earth's magnetic field during measurement. The problem of circumferential shielding currents in the parallel gradiometer pick-up loop is solved by the use of an appropriately designed magnetometer SQUID integrated on the gradiometer chip. The magnetometer's feedback coil of the flux-locked loop is laid out as a small Helmholtz coil pair, thus keeping the homogeneous magnetic field constant for both the magnetometer and the gradiometer. Therefore, the balance of the directly coupled gradiometer SQUID is enhanced from 100 up to 3800. The noise limited magnetic field gradient resolution of 45 pT m−1 Hz−1/2 is preserved down to frequencies of several Hz even after strong motion in the Earth's magnetic field.

Cryogenic bolometers are adequate sensing devices for sub-millimeter observations. They are used for instrumentation in radio telescopes like the Atacama Pathfinder Experiment (APEX), which is a 12-m radio telescope in Chile's Atacama desert. Through its thin and dry atmosphere, star formation in the red-shifted early universe can be observed. A suitable bolometer has a high sensitivity and consists of several tens to hundreds of pixels that are combined to an array. To meet these requirements, we use transition edge sensors. They detect radiation by measuring a temperature increase in an appropriate absorber. For highest sensitivity, the absorber is only in weak thermal contact to its surroundings. This is achieved by placing it on a SiN membrane that is structured to further decrease the thermal coupling. A superconductor that is biased at its transition temperature serves as thermometer for the transition edge sensor. We present the fabrication of such devices and discuss encountered difficulties. Further, we briefly describe the incorporation of a sensor chip with an array of 39 pixels into an instrument that currently operates at APEX. For the fall of 2010 the installation of a 300 pixel array is scheduled.

Nowadays detection systems based on superconducting nanowire single-photon detectors (SNSPD) are mainly with a single-pixel detector. Multi-pixel systems would extend the field of possible applications. Therefore, new concepts are required for effective readout of multi-pixel SNSPDs. We give an overview of possible concepts, conditions of operation and dedicated effort to optimize the requirements of different applications in the single-photon regime.

Since 2007 we are developing passive submillimeter-wave video cameras for persona l security screening. Incontradiction to established portal-based millimeter-wave scanning techniques, t hese are suitable for stand-o or stealth operation. The cameras operate in the 350GHz band and use arrays of superconducting transition-edge sensors (TES), reector optics, and opto-mechanical scanners. Whereas the basic principl e of these devicesremains unchanged, there has been a continuous development of the technical details, as the detect or array, thescanning scheme, and the readout, as well as system integration and performance. The latest prototype of thiscamera development features a linear array of 128 detectors and a linear scanner capable of 25Hz frame rate.Using di erent types of reector optics, a eld of view of 1 2m 2 and a spatial resolution of 1{2cm is providedat object distances of about 5{25m. We present the concept of this camera and give detai ls on system designand performance. Demonstration videos show its capability for hidden threat detectio n and illustrate possibleapplication scenarios.Keywords: submillimeter-wave, THz, terahertz, camera, imaging, video, bolometer, TES

As manmade space debris in the low earth orbit becomes an increasing risk to space missions, which could even result in total mission loss, it has become even more critical to have detailed knowledge of the properties of these particles like the mass, the velocity and the trajectory. In this paper, we present a newly designed, highly sensitive impact detector array with 16 pixels for space debris analysis. The thermopile sensor array, which was developed in the project, consists of 16 miniaturized multi-junction thermopile sensors made by modern thin-film technology on Si wafers. Each thermopile sensor consists of 100 radially arranged junction pairs formed from evaporated antimony and bismuth thin films. The centrally located active (hot) junctions comprise the active area of 1 mm². The output e.m.f. of the sensor is proportional to the temperature difference between the active and the reference junctions. The thermopile requires no cooling and no bias voltage or current for operation. It generates no 1/f noise but only the thermal resistance (Nyquist) noise. The sensor can be used for DC and low frequency AC measurements. The impact energy of micro sized particles is measured by a calorimetric principle. This means that the kinetic energy of the particle is converted into heat by hitting the absorbing foil, which is glued on the surface of the membrane area. This setup in combination with a preceded velocity detector allows the measurement of the most interesting particle quantities mass, velocity and trajectory.

The mapping of the Earth's magnetic field or field gradient is a proven method in surface exploration and archaeometry. Caesium vapour magnetometers show the best magnetic field resolution of commercial devices, but their sampling frequency is limited to 10 Hz. Using SQUIDs it is possible to achieve the same or even better magnetic field resolution with a sampling frequency as high as 100 Hz or more. This allows significantly shorter acquisition times, which is essential for the mapping of large objects. In this paper we check the performance of our developed systems on a neolithic double-ring ditch enclosure near Weimar, Germany. We compare mappings of this area using an electronic caesium gradiometer, an electronic HTS SQUID gradiometer and an integrated planar LTS SQUID gradiometer. With all three systems the magnetic pattern of the ditch is visible; however, the electronic HTS gradiometer shows disturbances of the same order of magnitude as the gradient signal of the ditch, due to an insufficient common mode rejection whilst being moved. The planar LTS SQUID gradiometer shows superior performance. Its mapping shows a much better contrast and features that are not visible in the mapping of the caesium gradiometer.

Following an established concept of IR spectroscopy, the total absorber was transferred to the THz wavelength. This allows for measurement of effects interesting for life-science applications like DNA hybridization and molecular resonances. The complete process from simulations to measurements will be addressed.

Passive submillimeter wave imaging is a concept that has been in the focus of interest as a promising technology for security applications for a number of years. It utilizes the unique optical properties of submillimeter waves and promises an alternative to millimeter-wave and X-ray backscattering portals for personal security screening in particular. Possible application scenarios demand sensitive, fast, and fleixible high-quality imaging techniques. Considering the low radiometric contrast of indoor scenes in the submillimeter range, this objective calls for an extremely high detector sensitivity that can only be achieved using cooled detectors. Our approach to this task is a series of passives standoff video cameras for the 350 GHz band that represent an evolving concept and a continuous development since 2007. The cameras utilize arrays of superconducting transition-edge sensors (TES), i.e. cryogenic microbolometers, as radiation detectors. The TES are operate at temperatures below 1K, cooled by a closed-cycle cooling system, and coupled to superconducting readout electronics. By this means, background limited photometry (BLIP) mode is achieved providing the maximum possible signal to noise ratio. At video rates, this leads to a pixel NETD well below 1K. The imaging system is completed by reflector optics based on free-form mirrors. For object distances of 3–10m, a field of view up to 2m height and a diffraction-limited spatial resolution in the order of 1–2cm is provided. Opto-mechanical scanning systems are part of the optical setup and capable frame rates up to 25 frames per second. Both spiraliform and linear scanning schemes have been developed.

We present a newly designed thermoelectric detector chip of high detectivity for the space mission BepiColombo to Mercury. The sensor is part of the MERTIS radiometer, which enables radiometric measurements in the spectral range from 7-40 micron to study the thermo-physical properties of the planet's surface material. In collaboration with the DLR Institute of Planetary Research, the Institute of Photonic Technology has developed a sensor array with a specific detectivity D* of 1.3 x 10 9 Jones in vacuum environment and 2 x 15 individual readable channels. In addition, it has an optical slit in the middle, which serves as the entrance slit of a spectrometer downstream. The sensor area is coated with an absorbing layer, in this case silver black having an absorption coefficient of nearly 100 percent in a wavelength range from 0.4 up to 20 micron. To minimize the thermal cross talk between the individual pixels, each pixel is separated by a 50 micron slit in the self-supporting silicon nitride membrane. For good mechanical stability of the pixels, the pixel membrane is tensioned by 10 micron bridges like braces. The sensor is electrically contacted with a star-flex PCB by direct wire bonding and both are mounted on milled aluminum housing. At the Institute of Photonic Technology (IPHT), high detectivity radiation sensors are developed and based on the thermoelectric principle. The thermoelectric materials used are the highly effective combination of n-bismuth(87%)- antimony(13%) / p-antimony. The sensors are designed, in the main, as miniaturized multi-junction thermocouples and made by state of the art thin film technologies allowing for achievable and reproducible detectivities D* in the range of 10 8 up to 2 x 10 9 Jones.

Here we report a laser plasma-driven source of T-rays with the highest pulse energy ever recorded in a laboratory. T-rays are emitted from the rear surface of a solid target in the non-collinear direction at incident laser intensities ~ 1019 W/cm2. Pulse energy measurements reported T-ray pulses with peak energies no less than 700 μJ. Temporal measurements using a single-shot electro-optic method showed the presence of sub-picosecond T-ray pulses with 570 fs duration, thus rendering the peak-power of the source higher even than that of state-of-the-art synchrotrons. A conversion efficiency of higher than 10−3 and an average power of 7 mW makes it the most efficient compact and powerful THz source known today. Spectral analysis revealed the presences of frequencies ranging from 0.1 − 133 THz, while most of the energy is localised in the low frequency region. The dependence of T-ray yield on incident laser energy is linear and shows no signs of saturation. The spatial distribution of the recorded T-rays indicates that most of the T-rays are emitted in the non-collinear direction from the rear-surface of a solid target and the contribution in the forward direction is very small. 2D particle-in-cell simulations show the presence of transient current at the target rear surface.

The performance of an optically pumped Mx magnetometer with miniaturized Cs cell at earth's magnetic field strength (50 μT) is investigated. Operation using detuned high intensity laser light is shown to be superior to the conventional resonant operation in terms of the projected shot-noise-limited ( 50 fT/√Hz) and the actual noise-limited sensitivity using a noise compensation method. The Zeeman light shift effect, emerging due to the off-resonant circularly polarized laser radiation and leading to a strong orientational dependence of the measurement, is suppressed by averaging two identical magnetometer configurations pumped with oppositely circularly polarized light. A residual heading error within the range of 14 nT, limited by the present experimental characterization setup, was achieved.

We have developed a cryogenic measurement system for single-photon counting, which can be used in optical experiments requiring high time resolution in the picosecond range. The system utilizes niobium nitride superconducting nanowire single-photon detectors which are integrated in a time-correlated single-photon counting (TCSPC) setup. In this work, we describe details of the mechanical design, the electrical setup, and the cryogenic optical components. The performance of the complete system in TCSPC mode is tentatively benchmarked using 140 fs long laser pulses at a repetition frequency of 75 MHz. Due to the high temporal stability of these pulses, the measured time resolution of 35 ps (FWHM) is limited by the timing jitter of the measurement system. The result was cross-checked in a Coherent Anti-stokes Raman Scattering (CARS) setup, where scattered pulses from a β-barium borate crystal have been detected with the same time resolution.

We compare the performance of two methods for the synchronization of the atomic spins in optically pumped magnetometers: intensity modulation of the pump light and the classical M(x) method using B(1) field modulation. Both techniques use the same set-up and measure the resulting features of the light after passing a micro-fabricated Cs cell. The intensity-modulated pumping shows several advantages: better noise-limited magnetic field sensitivity, misalignment between pumping and spin synchronization is excluded, and magnetometer arrays without any cross-talk can be easily set up.

Raman scattering spectroscopy allows the direct and fast study of molecules by analysis of their vibrational normal modes. However, for certain materials the scattered signal is superimposed by fluorescence, which - if present - overwhelms the intrinsically weak Raman signal by orders of magnitude. An approved method to resolve the instantaneous Raman signal of interest from the delayed fluorescence background is time-correlated single-photon counting (TCSPC). For that, a single-photon detector with fast dynamics is required. The, so-called, superconducting nanowire single-photon detector (SNSPD) is a promising candidate for TCSPC. We have developed an optical instrument using such a SNSPD for the TCSPC method. The detector is made from a 5 nm thick NbN film, patterned by electron-beam lithography in a meander line with a width of 100 nm and a filling-factor of 50 %, covering an active area of 4 × 4 μm2. As a proof of concept we have shown that it is possible to resolve low power optical signals (λ between 520 and 630 nm) with a timing jitter of about 35 ps. Based on our experimental results we will discuss perspectives and limits of SNSPD application for spectroscopy.

A newly designed highly detective intra-slit thermoelectric room-temperature linear array is presented. The thermoelectric sensor array ZS-64-2 with 64 individually readable channels was designed and developed for IR spectroscopy. It is suitable for analytical measurement technology, for example, in determining the age of technical oils in real time. For this, the selected absorption bands of the oil are analyzed and evaluated. This allows conclusions be drawn about the condition of lubricants and coolants, so that they can be replaced when it is needed. This method helps to save valuable resources and it helps to avoid costly damages. In order to achieve the high detectivity of D* = 1.8 x 109 Jones the sensor was designed and optimized to be operated under vacuum conditions. For minimizing the thermal cross talk between the individual pixels, they are separated from each other by a 50 micron slit in the self-supporting silicon nitride membrane, which has a thickness of nearly 1 micron.

Against a background of newly emerged security threats the well-established idea of utilizing submillimeter-wave radiation for personal security screening applications has recently evolved into a promising technology. Possible application scenarios demand sensitive, fast, flexible and high-quality imaging techniques. At present, best results are obtained by passive imaging using cryogenic microbolometers as radiation detectors. Building upon the concept of a passive submillimeter-wave stand-off video camera introduced previously, we present the evolution of this concept in a practical application-ready imaging device. This has been achieved using a variety of measures such as optimizing the detector parameters, improving the scanning mechanism, increasing the sampling speed, and enhancing the camera software. The image generation algorithm has been improved and an automatic sensor calibration technique has been implemented taking advantage of redundancy in the sensor data. The concept is based on a Cassegrain-type mirror optics, an opto-mechanical scanner providing spiraliform scanning traces, and an array of 20 superconducting transition-edge sensors (TES) operated at a temperature of 450-650 mK. The TES are cooled by a closed-cycle cooling system and read out by superconducting quantum interference devices (SQUIDs). The frequency band of operation centers around 350 GHz. The camera can operate at an object distance of 7-10 m. At 9m distance it covers a field of view of 110 cm diameter, achieves a spatial resolution of 2 cm and a pixel NETD (noise equivalent temperature difference) of 0.1-0.4 K. The maximum frame rate is 10 frames per second.

Due to its high molecular specificity, Raman spectroscopy is a well-established analytical tool. Usually the inelastically scattered Raman light is spectrally dispersed by a spectrometer. Here, we present an alternative method, using an optical fiber as dispersive element. As the group velocity within the fiber is wavelength-dependent, different Raman bands arrive at different times at the detector. In combination with time-correlated single-photon counting, Raman spectra can be measured in the time domain. As detector we implemented a Superconducting Nanowire Single-Photon Detector (SNSPD), which possesses a timing accuracy of about 20 ps. Within this contribution we show first results of Raman spectra measured in the time domain using gradient index fibers of varying length.

We present a novel concept to trim the transmission properties of finite two dimensional photonic crystal slab waveguide structures by UV photobleaching. Systematic fabrication inaccuracies may be compensated due to the shift of the spectral properties during the bleaching process. To prove our concept experimentally, we measured the transmission of UV sensitive photonic crystal structures for different doses. A shift of band edges and defect resonance peaks depending on UV dose is observed due to changes in refractive index and geometry.

We present a novel concept to trim the transmission properties of finite two dimensional photonic crystal slab waveguide structures by UV photobleaching. Systematic fabrication inaccuracies may be compensated due to the shift of the spectral properties during the bleaching process. To prove our concept experimentally, we measured the transmission of UV sensitive photonic crystal structures for different doses. A shift of band edges and defect resonance peaks depending on UV dose is observed due to changes in refractive index and geometry.

We present a concept for a time-tagged multiplexed readout of several superconducting nanowire single-photon detector elements for small arrays in ultra-short pulsed laser applications. The detector elements were coupled in an array by a superconducting delay line giving each detector element a temporal signature. The complete detector chain is biased by one bias supply. The patterning concept and the first experimental proof of principle are demonstrated on two-detector element arrays with delay times of 86 and 156 ps each made from a 5-nm NbN film on sapphire. We discuss the propagation delay of a delay line taking the geometric and kinetic inductance into account. We show that mainly the normal conducting propagation velocity defines the characteristic time of the delay line and that the inductance dependent response pulse width currently limits the maximum number of detector elements.

Against a background of newly emerged security threats, the well-established idea of utilizing submillimeter-wave radiation for personal security screening applications has recently evolved into a promising technology. Possible application scenarios demand sensitive, fast, flexible and high-quality imaging techniques. At present, best results are obtained by passive imaging using cryogenic microbolometers as radiation detectors. Building upon the concept of a passive submillimeter-wave stand-off video camera introduced previously, we present the evolution of this concept into a practical application-ready imaging device. This has been achieved using a variety of measures such as optimizing the detector parameters, improving the scanning mechanism, increasing the sampling speed, and enhancing the image generation software. The camera concept is based on a Cassegrain-type mirror optics, an optomechanical scanner, an array of 20 superconducting transition-edge sensors operated at a temperature of 450 to 650 mK, and a closed-cycle cryogen-free cooling system. The main figures of the system include: a frequency band of 350±40 GHz, an object distance of 7 to 10 m, a circular field of view of 1.05 m diameter, and a spatial resolution in the image center of 2 cm at 8.5 m distance, a noise equivalent temperature difference of 0.1 to 0.4 K, and a maximum frame rate of 10 Hz.

Digital superconducting quantum interference devices (SQUIDs) have been proposed to extend the dynamic range of analog SQUIDs whenever magnetic fields varying in a wide range need to be measured. We developed a digital SQUID concept, based on the single flux quantum technique, using the reliable 1 kA/cm2 niobium trilayer technology of the FLUXONICS Foundry. We present an extensive experimental analysis to evaluate the digital SQUID magnetometer operation in shielded and unshielded conditions. Bit error rate measurements have shown reliable operation of the digital superconducting circuitry with operation margins of ±11%, confirmed by stable operation in unshielded magnetometer mode for more than 10 h. The best intrinsic magnetic field resolution, corresponding to one magnetic single flux quantum (Φ0), was found to be about 4.2 nT. Peak-to-peak amplitudes of 14 800 and 2810 flux quanta Φ0 could be measured, respectively, for inductively coupled current and magnetic field inputs. A flux noise level of 220 mΦ0/Hz at 0.1 Hz has been measured, corresponding to a dynamic range of 76 dB (e.g., above 12 bits). Furthermore, preliminary experiments have shown that the integration of a digital SQUID with an analog dc SQUID in a hybrid magnetometer is a solution to reach simultaneously a high dynamic range and an increased field sensitivity. Such a device is of utmost importance to detect magnetic fields with high dynamic range to monitor earthquakes in the presence of high amplitude external magnetic perturbations.